The Adaptive Contoured Window Processing Method For ESPI And InSAR

Electronic Speckle Pattern Interferometry (ESPI) is a whole-field non-destructive technique to measure optical rough surfaces. It is widely used in the measuring of vibration, displacement, strain and medical diagnosis. Interferometric Synthetic Aperture Radar (InSAR) is a new technology developed from the technology of Synthetic Aperture Radar (SAR). And it is mainly used to obtain the Digital Elevation Model (DEM) in a vast area precisely and to monitor minute changes of the ground surface. These two techniques are closely related although different. Both of them take interferograms as their main object of research and aim to get high quality fringes so as to get good whole-field phases, based on which the wanted physical parameters will be calculated. So fringe processing is a key step for both techniques by influencing their precisions and applications. Based on a thorough exploration into these two kinds of fringe processing techniques, this dissertation presents its originality in the following aspects:(1) The merits and shortcomings of two fringe-orientation obtaining methods, including the plane-fit method and the gradient method, are well studied. And they are combined to overcome their disadvantages so as to get more precise orientation results. The accumulated variance method is also put forward to calculate fringe orientations. Based on the analyzing of ESPI and InSAR fringe characters, this dissertation proposes two ESPI fringe-density estimating methods including the accumulated difference method and the fringe skeleton method, and two InSAR fringe-density estimating methods including the binary fringe method and the gradient-based method. Fringe orientation and fringe density are two kinds of important information for the following researches in this dissertation.(2) Two methods of defining a contoured window are carried out. One is the method based on orientation and gradient and the other is the skeleton-distance averaging method. Experiments show that the contoured windows obtained with these two methods are more precise than those obtained with original ones. Contoured window is also important for the following researches.(3) Based on the contoured window filter (CWF) and the estimations of fringe orientation, an adaptive contoured window filter (ACWF) is realized for ESPI interferograms. The ACWF can shift its shape to the changes of fringe orientation and alter its size to the changes of fringe density. In this way, noise can be depressed better while the fringes being kept well. Combined with the adaptive contoured window, the contoured correlation interferometry (CCI) method is also developed by making its window size adaptive. In this way, the CCI method can be more adaptive and applicable and can get better correlation results for both wide and thin fringes at the same time. (4) The application of CWF for InSAR fringes are proposed and well studied. This filter is proved theoretically and experimentally to be better than both the sine/cosine filter and the Lee filter. Combined with CWF and the estimation of InSAR fringe density, adaptive window filter for InSAR is achieved so as to filter noise better while keeping fringes well.(5) This dissertation also proposes a method to locate skeletons and calculate the sign map according to the fringe gradient angles. Both the results and the resistance to noise are better than those of the original methods. A method of completing skeletons along fringe orientations is carried out, and the fringe-normalizing method and the quadrature transform method are refined to calculate phase from one filtered ESPI image. A fast quality-guided phase unwrapping method is researched. This technique shortens the processing time in a great deal and is significant when dealing with vast InSAR data. A method of quality-guided phase unwrapping based on contoured window judge is also proposed to enhance the unwrapping reliability.